Deceleration energized load controlled brake valve

ABSTRACT

A combination valve assembly for a dual circuit brake system in which a metering valve is in one circuit, a proportioner is in the other circuit, and a hydraulically reset pressure loss warning indicator unit is sensitive to both circuits. The proportioning action rates change to match vehicle loading, to accommodate uphill and downhill grades, and to accommodate any brake fade. This is accomplished providing a deceleration sensing mechanism which locates the proportioner piston to determine the amount of proportioning required based on the pressure at which deceleration triggers an inertia valve in the proportioner. Actuation of the warning unit because of pressure loss in the metering valve circuit causes the proportioner to be overridden by removing a valve element from a closed position to permit direct flow so that pressure through the proportioner is not proportioned.

United States Patent 91 Shellhause DECELERATION ENERGIZED LOADCONTROLLED BRAKE VALVE [75] Inventor: Ronald L. Shellhause, Vandalia,

[4 1 Apr. 17, 1973 Primary Examiner-M Henson Wood, Jr. AssistantExaminer-.lohn J. Love Att0rneyW. E. Finken et a].

[57] ABSTRACT A combination valve assembly for a dual circuit brakesystem in which a metering valve is in one circuit, a proportioner is inthe other circuit, and a hydraulically reset pressure loss warningindicator unit is sensitive to both circuits The proportioning actionrates change to match vehicle loading, to accommodate uphill anddownhill grades, and to accommodate any brake fade. This is accomplishedproviding a deceleration sensing mechanism which locates theproportioner piston to determine the amount of proportioning requiredbased on the pressure at which deceleration triggers an inertia valve inthe proportioner. Actuation of the warning unit because of pressure lossin the metering valve circuit causes the proportioner to be overriddenby removing a valve element from a closed position to permit direct flowso that pressure through the proportioner is not proportioned.

4 Claims, 1 Drawing Figure PATENTEI] APRI 7 I975 DECELERATION ENERGIZEDLOAD CONTROLLED BRAKE VALVE SUMMARY OF THE INVENTION The inventionrelates to a vehicle dual circuit com bination valve assembly, and moreparticularly to one having a pressure loss warning unit and aproportioner unit with proportioner override, the proportioning actionbeing modified by deceleration sensing. The override action occurs whenpressure loss occurs in the brake circuit not containing theproportioner, and in an uncorking type of action in which a normallyclosed valve element is moved away and out of engagement with themovable proportioner element to permit direct and unproportioneddelivery of brake pressure through the proportioner. By use of thedeceleration sensing mechanism, the proportioning rates change toaccommodate variations in vehicle loading without requiring physicalattachment to the vehicle suspension system, thereby effectivelysimulating load sensing. Brake fluid is permitted to pass uninhibited tothe rear brakes during brake apply until sufficient deceleration isobtained to energize the inertia valve within the proportioner piston.During the initial pressure buildup, prior to deceleration energization,the proportioner piston moves toward the front of the assembly due todifferential areas exposed to the brake supply pressure. The amount ofpiston movement having taken place when deceleration energization occurssets the amount of displacement that the proportioner is capable ofproducing. When deceleration energization occurs, the inertia valvecloses, the proportioner piston direction of movement is reversed, anddisplacement proportioning action begins. When the vehicle is lightlyloaded deceleration energization occurs more quickly since the samebrake pressure will establish a higher deceleration rate under thatcondition than it will for a heavily loaded vehicle. Therefore, theinitial forward travel of the proportioner piston is small andproportioning takes place at a lower pressure gradient. For heavyvehicle loads the proportioner piston will initially move furtherforward and a multiplier piston comes into play upon decelerationenergization to provide increased rearwardly acting thrust and increasethe pressure gradient at which proportioning takes place.

IN THE DRAWING The single FIGURE illustrates mechanism embodying theinvention, with parts in section, and with a schematic showing of thebrake system and warning circuits.

DESCRIPTION OF THE PREFERRED EMBODIMENT The housing is provided with athrough bore 12 having several shoulders thereon and divided intoseveral chambers as will be described. The front brake pressure inlet 14connects with a left center portion of the bore 12, and outlets l6 and18 connect with the left end portion of the bore 12. These outlets areconnected to the two front disc brakes 20 and 22 of the vehicle. Therear brake pressure from the master cylinderv 24 passes through inlet26, connected to the right center portion of the bore 12, and the outlet28 at the right end of the bore 12 is connected to the rear brakes 30and 32.

The left portion 34 of the assembly comprises the metering section,which prevents initial front disc brake pressure buildup until the rearbrake shoes contact the drums. The pressure thus held off is thenadmitted to the front brakes at higher input pressures.

The center portion 36 of the assembly comprises a warning sectionincluding a latch-type hydraulic reset warning switch assembly andactuator. The switch assembly 38 is threaded into a housing opening 40so that the switch plunger 42 extends into the center portion of thehousing bore 12.

The right portion 44 of the assembly includes a proportioner sectioncomprising a rear brake pressure proportioner, a proportioner overridearrangement, and deceleration sensing and control mechanism.

METERING SECTION Front brake pressure enters inlet 14 and chamber 46,provided in a part of bore 12. The left side of chamber 46 is defined bythe valve pin stop 48. This stop is cup shaped, and is provided with oneor more openings 50 through which chamber 46 is connected to the chamber52 inside the cup. The metering valve pin 54 has a smooth head 56positioned in chamber 52 and separated by a groove from a knurled pinsection 60. The pin extends leftwardly to a reduced pin section 62 aboutwhich diaphragm seal 64 is mounted. The pin 54 is slidably mounted in abore formed through the valve plug 70. The pin reduced end 72 extendsoutwardly through the valve plug and is covered by the metering valveboot 74. The valve plug is held in the left end of the housing bore byretainer ring 76.

The chamber 78 between diaphragm seal 64 and the valve pin stop 48contains the metering valve 80. The outer portion 82 of valve acts as avalve which sealingly engages a valve seat 84 formed by the valve pinstop 48 and a shoulder 86 of bore 12. The annular portion of meteringvalve 80 has an axially extending annular section or lip 88 which (inthe position shown) receives and engages the outer periphery of the pinknurled land 60. A valve retainer and spring seal 90 presses against theother side of metering valve 80 relative to valve pin stop 48 and isengaged by compression spring 92, which also acts against spring seat 94and the outer periphery of diaphragm seal 64. The portion of pin 54intermediate land 60 and section 62 has a groove receiving a spring seat98. Spring seats against spring seats 94 and 98 and urges pin 54rightwardly toward engagement by the end of head 56 with pin stop 48.The front brake pressure outlets 16 and 18 connect with chamber 78.

When brake pressure is initially applied, fluid passes through inlet 14,chamber 46, passages 50, chamber 52, and the axially grooved openingsformed by the knurled land 60, to chamber 78. This initial pressure maybe between 0 and 30 psi, for example. This light initial pressure inchamber 78 is transmitted to the front brakes 20 and 22 and also acts ondiaphragm seal 64 to move metering valve pin 54 to the left againstspring 100 until the shoulder of the knurled land 60 engages the innerannulus of spring retainer 90. This provides a first stop for the pin54, at which time the smooth outer periphery of pin head 56 has moved toengage the lip 88 of the metering valve 80, blocking off further flow offluid from chamber 52 to chamber 78.

Additional inlet pressure must now be built up before additionalpressure can be supplied through the valve assembly to the front brakes.Thispressure is called the hold-off" pressure and is controlled by theeffective area of the metering valve 80 and the load of spring 92. Thehold-of pressure may be varied from about 60 to 200 psi as required fora particular vehicle.

Continued increase in inlet pressure in chambers 46 and 52 acts on theeffective area of the metering valve 80 and the head 56 of the meteringvalve pin 54 and eventually causes the pin 54, the valve 80, and thespring retainer 90 to move leftwardly against the forces of springs 92and 100 to open the valve 82 relative to its seat 84. Inlet pressure isthen admitted to chamber 78 past the outer periphery of valve seal 80and acts on diaphragm seal 64 to move pin 54, with retainer 90 and valve80, further to the left until a pin land in plug 70 engages the shoulderat the left end of the bore of plug 70. A transition between the inletpressure and the pressure to the front brakes takes place as this occursand this transition is completed at a pressure point called the blendpressure. The inlet pressure is thereafter the same as the pressurepassing through outlets l6 and 18 to the front brakes. The blendpressure is controlled by the relationship of the effective area ofdiaphragm seal 64 and the spring load of springs 92 and 100.

Upon release of inlet pressure, pin 54 gradually moves rightwardly as dovalve spring retainer 90 and valve 80, until the metering valve 80 againhas its periphery 82 seating against the valve seat 84. As furtherrelease of inlet pressure occurs, the lip 88 of the metering valve liftsto allow pressure to flow from chamber 78 to chamber 52. This allowsrelease of pressure to the front brakes 20 and 22 at a very smallpressure differential. Upon complete release, pin 54. assumes theposition shown so that chamber 78 is again connected to chamber 52through the grooves formed by the knurls of pin land 60.. These knurlsand grooves provide free flow of brake'fluid for compensation of changein volume of the hydraulic circuit due to thermal changes.

WARNING SECTION The switch assembly 38 is threaded into an appropriateopening 40 in housing 10. A terminal 110 extends outwardly and iselectrically connected through a suitable switch 116 to an indicator 118and a source of electrical energy schematically illustrated as battery120. Indicator 118 maybe a light, bell, or horn, by way of example.Plunger 42 closes a switch in assembly 38 when moved upwardly tocomplete an electrical connection between the grounded housing andterminal 110, and opens the switch when it moves downwardly.

The switch piston assembly 136, including piston 138, is positioned inthe center portion of the bore 12 of housing 10 so that the pistongrooved center section 140 is normally aligned with plunger 42, theplunger end being held in groove 140 by the force ofa spring in theswitch assembly 38. The groove has beveled sides leading to theshoulders and so positioned that move-' ment of piston assembly 136 toeither a leftwardly or rightwardly direction causes plunger 42 to becammed upwardly to close the switch in assembly 38. The switch is heldin the closed position by engagement of the lower end of plunger 42 onone of the shoulders. The slightly larger lands of the shoulders aid inholding plunger 42 on a shoulder once it has been positione there.

The right end of piston 138 is formed as an enlarged land 154 providedwith a seal.156. Land 154 and seal 156 guide and seal piston 138 in theright center position of bore 12. The left end of piston 138 has a land158 of the same diameter as land 154 and guides piston 138 in theleftcenter portion of bore 12. The left outer end 160 of the pistonassembly is formed as a land 162 of smaller diameter than lands 154 and158. A seal retainer 164 slidably fits over land 162 and has a smallerinner diameter than the diameter of lands 154 and 158, but a largerouter diameter than the diameter of those lands. For this purpose, thehousing bore 12 is provided with a shoulder 166 against which retainer164 normally is abutted. An O-ring seal 168 is received about the land158 intermediate the retainer 164 and another sleeve-like retainer 170.Retainer 170 has the same inner and outer diameters as retainer 164.Retainers 164 and 170 and the seal 168 may move relative to piston 138under certain conditions. I

The left end 160 of piston 138 and one side of retainer 170 are exposedto master cylinder front brake pressure in chamber 46. The right end1540f piston 138 is exposed to master cylinder rear brake pressure inchamber 172. Rear brake pressure inlet 26 is connected to the mastercylinder 24 and to chamber 172.

The piston assembly 136 also has a recess or bore 174 formed in theright end of piston 138 and opening into chamber 172. Spring 176 fits inthe inner end of bore 174 and seats on a guide 178 which is slidablyreceived in bore 174. Guide 178 may be in the form of a grooved land, ormay be a fluted member. In either case, it is secured to or formed as apart of a valve element of the proportioner section 44 described belowin detail. An inwardly lanced tab 180 adjacent the open end of bore 174provides a stop for guide 178 such that sufficient leftward movement ofpiston 138 will cause tab 180 to engage guide 178 and thereafter movethe guide leftwardly with further leftward movement of piston 138. Thisprovides a lost-motion connection discussed below.

So long as substantially normal front and rear brake pressures exist inchambers 46 and 172, the switch piston assembly 136 will be in'theposition shown. Should front brake pressure loss occur while rear brakepressure remains, the higher pressurein chamber172 acting on the rightend of piston 138 will move the piston assembly 136 leftwardly. Land 158will cause seal retainers 164 and 170, as well as seal 168, to also moveleftwardlywith piston 138; This movement will move plunger 42 upwardlyand over oneof the adjacent lands until it rests on one of the adjacentshoulders. This will hold switch of assembly 38 closed, holding thewarning circuit in the energized condition. When, for example, switch116 is the vehicle ignition switch, indicator 1 18 will be energized solong as the ignition switch is closed and piston 138 remains in theactuated condition.

The warning'section is hydraulically reset when the front brake systemis repaired and front brake pressure is again applied in chamber 46.This pressure will act against the larger combined effective areas ofseal retainer 170 and the left end 160 of piston 138 (as compared to theeffective area of the right land of piston 138) to move piston assembly136 rightwardly until the seal retainer 164 again engages the shoulder166. This recenters the piston assembly and opens the warning switch ofassembly 38.

Should rear brake pressure fall substantially below front brakepressure, the piston 138 moves rightwardly, with plunger 42 movingupwardly over the other adjacent land and resting the other adjacentshoulder. When the rear brake pressure is again available in chamber172, the larger effective area of the right end of piston 138 relativeto the effective area of the piston left end 160 permits rear brakepressure to move the piston 133 to the left until its land 158 engagesretainer 164. Thus, the position shown is again assumed.

PROPORTIONER SECTION The right end of the bore 12 through housing isformed to provide chamber 172 and a larger chamber 182. The shoulders184 and 186 separating the two chambers define with bore 12 anintermediate chamber 187. The proportioning valve cap member and housingsection 188 is threaded into chamber 182 and abuts against shoulder 184.Valve cap and housing section 188 has outlet 28 formed axially thereinand has a chamber 190 in its inner end to which the outlet 28 isconnected. The proportioning piston 192 is reciprocably received inchamber 190 and extends into chamber 182. Annular multiplier piston 194is reciprocably received in chambers 182 and 187, and receives one endof proportioning piston 192 therein.

The center flange 196 of piston 192 is piloted on the chamber wall 198of chamber 190. Thus, chamber wall 198 is a bore and piloting surface.The reduced diameter outer end 200 of piston 192 provides a mounting forcap 202, which is in the end of chamber 190 adjacent outlet 28. The endof cap 202 provides a stop for piston outer end 200, and is dimpled toform stops 204 which engage the end of chamber 190 adjacent outlet 28.Cap 202 is sufficiently smaller in diameter than chamber 190, and alsois located away from the chamber end due to the formation of stops 204,so as to provide for fluid connection between chamber 190 and outlet 28.Recess 206 formed in the inner end 208 of piston 192 has a recessedshoulder 210 to provide a seat for compression spring 212. The other endof spring 212 en- I gages spring seat 214, which abuts shoulder 186.Thus, in the assembled position, spring 212 urges piston 192 to theright so that it abuts cap 202 and is limited in its axially rightwardmovement by piston Stop 204.

Piston 192 has another recess or chamber 215 formed in its outer end 20in which the inertia mechanism is located. Chamber 215 is connected withrecess 206 by means of axial passage 216 and one or more offset passages217 which are parallel to passage 216. The end of passage 216 openinginto recess 206 is formed to provide a valve seat 218. Valve seat 218 isone valve element of the proportioner override valve. The valve stem 220extends through recess 206 of piston 192 and its outer end is providedwith a valve element 224 which mates with valve seat 218. The inner end226 of valve stem 220 extends into piston bore 174 and has guide 178formed thereon or secured thereto by suitable means. Thus, a lost motionconnection is provided between valve stem 220 and the switch piston 138.

A cross passage 230 in piston 192 intermediate recesses 206 and 215connects passage 216 with annular chamber 232, defined by wall 198 andthe outer surface of piston outer end 200 and being a part of chamber190. The end of passage 216 opening into recess 215 is formed to provideinertia valve seat 234. The inertia valve 236 is loosely positioned inrecess 215 for axial and transverse movement, with retainer 238 at theouter end of the recess 215 limiting its rearward movement and venturibaffle 240 at the inner end of the recess guiding and limiting itsforward movement. Baffle 240 has a generally semi-torus configurationwith the concave portion facing the ends of passages 217, and the innerperiphery 242 guiding and engaging the tapered valve element 244 formedas the forwardly extending part of inertia valve 236. The rearwardlyextending portion 246 of valve 236 is cup-shaped to receive inertia ball248. A finger-like valve release spring 250 is secured to the outersurface of piston end 200 by clip 252, the spring extending forwardly inchamber 232, through passage 230, and projecting into the portion ofpassage 216 forming seat 234 so that it is yieldingly engageable withvalve element 244 when that element seats on seat 234. Seals 254, 256and 258 are respectively provided on proportioner piston end 200, centerflange 196, and proportioner piston end 208.

Multiplier piston 194 has a through-bore 260 with the inner end 208 ofpiston 192 reciprocably received therein and sealed by seal 258. Flange262 on piston 194 receives spring seat 264 on one side thereof and mayabut shoulder 184 on its other side. A compression spring 266 has oneend engaging seat 264 and the other end engaging a seat 268, which ispositioned against a shoulder 270 formed on housing section 188 at therear end of chamber 182. The portion 272 of piston 194 forward of flange262 extends into chamber 187 and has seal 274 thereon sealingly engagingthe wall of chamber 187. An inner shoulder 276 in through-bore 260 isaxially aligned with the proportioning piston end 208.

The mechanism is in the position illustrated before brake pressure isapplied. Upon application of master cylinder rear brake pressure throughinlet 26 and into chamber 172, pressurized fluid passes through passages217 and 230 and chamber 190, past cup 202, and into outlet 28. As thepressure builds up, it acts on the annular piston area A A defined bythe area A of piston 192 exposed to chamber 190 less the piston Area A,exposed to bore 260, so as to move piston 192 to the left against theforce of spring 212. The spring rate of spring 212 is set to allowsufficient travel of piston 192 to the left to provide adequatedisplacement during the proportioning cycle. Since pressure is beingbuilt up substantially equally and normally in the front and rear brakesupply lines, the hydraulic forces do not move the switch piston 138.

The proportioning cycle begins when a predetermined deceleration isattained to trigger the inertia valve. This predetermined decelerationis controlled by the angle at which the assembly is mounted. In alightly loaded vehicle, it will occur well before piston 192 has movedsufficiently leftward to engage shoulder 276 of multiplier piston 194.When it occurs, valve element 244 moves forwardly through baffie innerperiphery 242, engages and moves the end of spring 250 forwardly, andseats against seat 234. This interrupts direct flow through theproportioner by way of passages 217 and chamber 215 to passage 230,chamber 232, around cup 202 and through outlet 28. Therefore, thepressure acting on area A -A tending to move piston 192 leftwardly doesnot increase further with further increases of pressure in chamber 172.Piston 192 stops its leftward travel and begins its proportioning actionby moving toward the right, displacing fluid through outlet 28 in aproportioning ratio which is a function of the spring load of spring 212and the relationship of area A -A acted upon by brake supply pressure toarea A A acted upon by brake apply pressure. When piston 192 engages cup202, which in turn is seated against the end of chamber 190 adjacentoutlet 28, the brake apply pressure out of outlet 28 remains constantwith further increases of brake supply pressure in chamber 172.

With a heavily laden vehicle, more brake pressure is required to obtainsufficient deceleration to trigger the inertia valve and piston 192moves leftwardly until its end 208 engages shoulder 276 of themultiplier piston 194. The contact of piston 192 with piston 194nominally occurs at the time deceleration produced by the pressure atthis point also triggers the inertia valve with the heavily ladenvehicle. When the free flow through the valve is stopped by activationof the inertia valve, the force of the multiplier piston 194 is added tothat of piston 192 as it moves to the right. This movement is now afunction of multiplier piston area A., and spring 212 as opposed by areaA and spring 266. The multiplier piston 194 and proportioner piston 192will move rightwardly as a unit until end 200 of piston 192 bottoms outon cup 202, with stop 204 engaging the end of chamber 190 adjacentoutlet 28.

With an intermediately laden vehicle, the piston 192 will initially moveleftwardly further than it does for a lightly laden vehicle but not asfar as it does for a heavily laden vehicle when deceleration triggersthe inertia valve. The piston 192 then moves rightwardly as before,proportioning by displacement at the light load rate but with a higherstarting pressure, until the multiplier piston, also moving rightwardly,catches up and makes contact with it. The output is then boosted by themultiplier piston and the ratio of supply pressure to apply pressurebecomes the same as in the heavily loaded vehicle condition but beginsat a lesser pressure.

Should the front brake pressure fall substantially below the rear brakepressure, additional work must be done by the rear brakes, and thisrequires additional rear brake pressure. To get the maximum brakingeffort under this condition and yet keep brake pedal effort as low aspossible, the action of the proportioner is overriden and held out ofthe system, Thus, when switch piston 138 moves leftwardly due to frontbrake pressure loss, the guide 178 is engaged by the tab 180 of piston138 and pulls the valve stem 220 leftwardly to open valve element 224well away from its seat 218. This forcible removal of the valve element224 from its normally closed position allows full rear brake pressure topass from chamber 172 through passages 216 and 230, and chamber 190, tooutlet 28, bypassing seat 234 and valve 244. The leftward movement ofpiston 192 is limited by the engagement of the piston end 208 withmultiplier piston shoulder 276, and end 272 of piston 194 with seat 264,which abuts housing shoulder 186. Thus, valve seat 218 cannot moveleftwardly a sufficient distance to close the direct connection ofchamber 172 with passage 216.

A vent groove 278 allows sufficient expansion of chamber 182 pastV-block seal 280 for proper proportioner function. Should either seal256 or 274 leak brake fluid to chamber 182, collection of fluid willtake place in groove 278. However, seal 280 will permit the release ofexcess fluid leakage collection to allow proper proportioner function.The seal 280 can also function as a vacuum bleeding seal, allowingvacuum bleeding of new cars on assembly lines.

it is an important aspect of the invention to provide structure whichmitigates the flow sensitivity of the inertia valve element 244 prior tothe deceleration triggering action. This is provided by locatingpassages 217 in such alignment with the torus interior of baffle 240that fluid flowing through passages 217 is directed through seat 234without exerting any flow-related effect on valve element 244 so long asit is in the position illustrated. However, when valve element 244 istriggered by deceleration to move through the baffle inner periphery 242and toward seat 234, flow of fluid aids in quickly seating the valveelement. Also, when the apply pressure is released, spring 250 will aidin moving valve 236 rearwardly, as will apply pressure in passage 216,returning the valve to the position shown.

What is claimed is:

1. A displacement type fluid pressure proportioner having an inlet andan outlet and comprising:

a first displacement piston having opposed effective differential areasone of which is subjected to an inlet pressure and the other of which isselectively subjected to the inlet pressure and an outlet pressure,

and first resiliently yieldable means urging said piston in an outletpressure increasing direction,

control means having a first control condition subjecting both of saidopposed effective differential areas to an increasing inlet pressurewhereby said first piston is moved against said first resilientlyyieldable means and outlet pressure is the same as inlet pressure, and asecond control condition disconnecting the other effective differentialarea from the inlet and subjecting it to the outlet pressure whereby thefirst mentioned first piston movement is stopped and further inletpressure increase moves said first piston in the opposite direction toincrease outlet pressure in a predetermined ratio with the increase ininlet pressure by displacement, second resiliently yieldable means and asecond piston having an effective area subjected to the inlet pressureurging it to move in the first piston opposite direction against saidsecond resiliently yieldable means and engageable with said first pistonat a point which is a function of the increase in inlet pressure and theinlet pressure at which said control means changes from said firstcontrol condition to said second control condition, said second pistonupon further increase in inlet pressure after engagement with said firstpiston exerting additional force on said first piston in said firstpiston opposite direction of movement.

2. The proportioner of claim 1 in which the inlet and outlet are adaptedto be connected in a vehicle hydraulic braking circuit to proportionbrake apply pressure to a hydraulically actuated brake to decelerate thevehicle, said control means comprising a vehicle deceleration ratesensing valve which moves from the open first control condition to theclosed second control condition when a predetermined vehicledeceleration rate is attained, and returns to the first controlcondition when the vehicle deceleration rate falls below thepredetermined vehicle deceleration rate.

3. The proportioner of claim 1 in which the inlet and outlet are adaptedto be connected in a first vehicle hydraulic braking circuit providingbrake supply pressure to the inlet to proportion brake apply pressurefrom the outlet to a hydraulically actuated brake to decelerate thevehicle, and means adapted to sense brake supply pressures in the firstvehicle hydraulic braking circuit and a second vehicle hydraulic brakingcircuit and acting upon a predetermined pressure differentialtherebetween characterized by a relative decrease in the second vehiclehydraulic braking circuit brake supply pressure to fluid connect saidinlet to said outlet through said first piston independently of saidcontrol means.

4. A brake apply pressure proportioner for a vehicle brake systemcircuit having a source of vehicle operator-controlled brake supplypressure, said proportioner comprising:

a housing having an axially extending bore therein, a

brake supply pressure inlet and a brake apply pressure outlet connectedwith said bore, said housing being axially oriented generallyfore-and-aft of the vehicle when installed therein;

a proportioner piston reciprocably received in one end of said boreadjacent said outlet and having a forwardly opening first recess in theforward end thereof and a rearwardly opening second recess in therearward end thereof;

first and second passage means connecting said first and secondrecesses;

first valve means normally closing said first passage means connectionto said first recess;

said piston having a flange between said ends of greater diameter thaneither of said ends and sealingly fitting said bore one end with saidpiston rearward end forming with said bore one end an annular chambercommunicating with said outlet;

means on said piston rearward end closing said second recess;

third passage means operatively fluid connecting said first passagemeans and said annular chamber;

a multiplier piston reciprocably received in the other end of said boreadjacent said inlet and having a stepped bore therethrough, saidproportioner piston forward end being reciprocably and sealinglyreceived in the larger portion of said stepped bore, said inlet being influid communication with said other bore end and with said stepped boreto provide brake supply pressure therein and in said proportioner pistonfirst recess; first spring means yieldably resisting forward movement ofsaid proportioner piston and second spring means yieldably resistingrearward movement of said multiplier piston;

deceleration rate sensing valve means sensitive to a predeterminedvehicle deceleration rate to close said first passage means connectionto said second recess and thereby fluidly disconnect brake supplypressure and brake apply pressure;

said brake supply pressure acting with said first spring means on saidproportioner piston in opposition to brake apply pressure acting thereonto displace said proportioner piston toward said out- -let and increasebrake apply pressure at a first proportionate rate from the pressure atthe time said deceleration rate sensing valve means closed saidconnection to a higher brake apply pressure determined by the amount ofdisplacement of said proportioner piston available as established by theamount of prior forward movement thereof under influence of brakepressure before said deceleration rate sensing valve means closed;

and means actuable under a predetermined vehicle brake system conditionto move said first valve means to open the connection of said firstpassage means to said first recess and establish brake supply pressurecommunication therethrough to said outlet independently of vehicledeceleration.

1. A displacement type fluid pressure proportioner having an inlet andan outlet and comprising: a first displacement piston having opposedeffective differential areas one of which is subjected to an inletpressure and the other of which is selectively subjected to the inletpressure and an outlet pressure, and first resiliently yieldable meansurging said piston in an outlet pressure increasing direction, controlmeans having a first control condition subjecting both of said opposedeffective differential areas to an increasing inlet pressure wherebysaid first piston is moved against said first resiliently yieldablemeans and outlet pressure is the same as inlet pressure, and a secondcontrol condition disconnecting the other effective differential areafrom the inlet and subjecting it to the outlet pressure whereby thefirst mentioned first piston movement is stopped and further inletpressure increase moves said first piston in the opposite direction toincrease outlet pressure in a predetermined ratio with the increase ininlet pressure by displacement, second resiliently yieldable means and asecond piston having an effective area subjected to the inlet pressureurging it to move in the first piston opposite direction against saidsecond resiliently yieldable means and engageable with said first pistonat a point which is a function of the increase in inlet pressure and theinlet pressure at which said control means changes from said firstcontrol condition to said second control condition, said second pistonupon further increase in inlet pressure after engagement with said firstpiston exerting additional force on said first piston in said firstpiston opposite direction of movement.
 2. The proportioner of claim 1 inwhich the inlet and outlet are adapted to be connected in a vehiclehydraulic braking circuit to proportion brake apply pressure to ahydraulically actuated brake to decelerate the vehicle, said controlmeans comprising a vehicle deceleration rate sensing valve which movesfrom the open first control condition to the closed second controlcondition when a predetermined vehicle deceleration rate is attained,and returns to the first control condition when the vehicle decelerationrate falls below the predetermined vehicle deceleration rate.
 3. Theproportioner of claim 1 in which the inlet and outlet are adapted to beconnected in a first vehicle hydraulic braking circuit providing brakesupply pressure to the inlet to proportion brake apply pressure from theoutlet to a hydraulically actuated brake to decelerate the vehicle, andmeans adapted to sense brake supply pressures in the first vehiclehydraulic braking circuit and a second vehicle hydraulic braking circuitand acting upon a predetermined pressure differential therebetweencharacterized by a relative decrease in the second vehicle hydraulicbraking circuit brake supply pressure to fluid connect said inlet tosaid outlet through said first piston independently of said controlmeans.
 4. A brake apply pressure proportioner for a vehicle brake systemcircuit having a source of vehicle operator-controlled brake supplypressure, said proportioner comprising: a housing having an axiallyextending bore therein, a brake supply pressure inlet and a brake applypressure outlet connected with said bore, said housing being axiallyoriented generally fore-and-aft of the vehicle when installed therein; aproportioner piston reciprocably received in one end of said boreadjacent said outlet and having a forwardly opening first recess in theforward end thereof and a rearwardly opening second recess in therearward end thereof; first and second passage means connecting saidfirst and second recesses; first valve means normally closing said firstpassage means connection to said first recess; said piston having aflange between said ends of greater diameter than either of said endsand sealingly fitting said bore one end with said piston rearward endforming with said bore one end an annular chamber communicating withsaid outlet; means on said piston rearward end closing said secondrecess; third passage means operatively fluid connecting said firstpassage means and said annular chamber; a multiplier piston reciprocablyreceived in the other end of said bore adjacent said inlet and having astepped bore therethrough, said proportioner piston forward end beingreciprocably and sealingly received in the larger portion of saidstepped bore, said inlet being in fluid communication with said otherbore end and with said stepped bore to provide brake supply pressuretherein and in said proportioner piston first recess; first spring meansyieldably resisting forward movement of said proportioner piston andsecond spring means yieldably resisting rearward movement of saidmultiplier piston; deceleration rate sensing valve means sensitive to apredetermined vehicle deceleration rate to close said first passagemeans connection to said second recess and thereby fluidly disconnectbrake supply pressure and brake apply pressure; said brake supplypressure acting with said first spring means on said proportioner pistonin opposition to brake apply pressure acting thereon to displace saidproportioner piston toward said outlet and increase brake apply pressureat a first proportionate rate from the pressure at the time saiddeceleration rate sensing valve means closed said connection to a higherbrake apply pressure determined by the amount of displacement of saidproportioner piston available as established by the amount of priorforwarD movement thereof under influence of brake pressure before saiddeceleration rate sensing valve means closed; and means actuable under apredetermined vehicle brake system condition to move said first valvemeans to open the connection of said first passage means to said firstrecess and establish brake supply pressure communication therethrough tosaid outlet independently of vehicle deceleration.